It's 6pm on a 122,000-ton ship off the coast of Finland, and I'm watching Sean Connery on the big screen playing a defecting USSR submarine commander in The Hunt for Red October. As he removes his beskozirka and grimly pours a vodka, the cinema sighs. Did Connery ever look more noble? But is that porthole he's standing in front of leaking?

Whoever programmed the films on this cruise has a sense of humour. The day before it was Captain Phillips, about the brutal hijacking of a container ship. Or was it Woody Allen's gin-soaked Blue Jasmine? Impossible to remember. The days merge into one long, light-headed forward-roll through time zones and oceans, breakfast becoming lunch becoming afternoon tea, and then early cocktails leading helplessly to a five- course dinner with flambéed lobster and balsamic strawberries, culminating in a live show by a Chinese magician who turns water into florescent-blue sand.

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There are 2,850 people onboard the 1,000ft Celebrity Eclipse: 13 decks, 1,426 staterooms, 10 restaurants (the creperie and Tuscan Grill are best), 12 bars, a gym, spa (excellent foot rubs), well-stocked library (Jane Eyre, The Dramatic Lives of the Emperors of Rome, Stephen King), lawn, shops, casino, grand theatre (where movies are screened four times a day), indoor and outdoor pools and bubbling hot tubs. It's a moving apartment complex, a starship destroyer. And while I confess I have often thought of such holidays as peculiar, to say the least (where to get a moment's peace?), in the week I'm onboard I scarcely spot an unhappy face among crew or passengers, or hear a voice raised in complaint or frustration.

Bedrooms are a good size and comfortable - private cubby-holes to flop in - and the ensuite bathrooms are kept spotless. Staff stop to talk, and take the same lifts as passengers; there is little sense of a smotheringly awkward upstairs-downstairs divide. In fact, the atmosphere is markedly benign and egalitarian. In the communal breakfast and lunch canteen, with its vast selection of bespoke omelettes, teriyaki salmon, tortillas, rare roast beef carved with formidable shows of expertise, pizzas, fresh bread, slabs of cake and elaborate ice-cream sundaes, some groups drink Champagne and toast each other while others quietly read Kindles in their flip-flops. There is something both pleasingly confidential and entirely random about travelling in such close quarters with perfect strangers.

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Although it's mostly couples in their fifties and sixties, there are some extended families travelling too. One evening a boy turns 17 and for a moment the whole crowd in the central atrium of the ship takes a break from dancing to the house band's version of 'Good Golly Miss Molly' to tipsily cheer him as he ascends the staircase, red as a beetroot.

The Eclipse travels all over the world, but this sold-out trip takes us from Stockholm to St Petersburg and then back through the Baltic towards Berlin and eventually Paris, stopping for city tours along the way. There is a particularly animated exodus to coaches and guides when we arrive in Russia for pre-arranged tours of St Petersburg, a place you still can't otherwise visit without a visa. It's been 25 years since I was last here; I came as a young teenager with the nuns from my convent school (Lord knows why they let us in, this was pre-Glasnost). And although there are now branches of Dior and Prada on Bolshaya Konyushennaya Ulitsa Square, the roads still throng with clapped-out Skodas. In food markets there is piped music of the kind once used to accompany those tiny, post-Khrushchev gymnasts who landed sensationally astraddle a beam, and women with arms like Brian Dennehy ladling Siberian honey from huge containers, occasionally tidying, with a nudge of fur bootees, the shoulder-high piles of oozing cherries that keep falling forward in a super-fragrant avalanche. Along the late-summer streets around Pushkinskaya station sheaves of fake flowers are sold next to bunches of real spring onions. Two huskies sleep as their master lays out fresh dill and sprigs of edelweiss on newspaper spread on the pavement.

That evening, back onboard, we set sail once more and there is a collective rubbing of hands. Passengers, now togged in satin gowns, anticipate a glass-blowing show, bourbon tasting and DJ Lenny playing the best of Neil Diamond. We are clearly mesmerised by the vastness of the wake of the ship. Cutting through the cadaverous grey waters at 24 knots, it moves inexorably on through the occasional shoal of flashing fish. It's a compulsive view and the soft shudder of the engines lullingly ever-present. Two days at sea stretch before us: nothing to do but thoroughly occupy this strange and hilarious world with its thousand treats laid on.

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This cruise is really a reboot of the holiday camp, but with black ties, Jacuzzis and watermelon Martinis, and I can't help but wonder how we must look from the outside at night, viewed through the countless portholes, in a massive mirage of delirium. The ironed shirts and lip gloss, the gentians on the tables in the crowded and cheerful banqueting halls, the frantic chatter and come-hither Hopperish glow of lights. And always along the top decks well after midnight, while staff are indoors laying tables for breakfast, couples wrapped in blankets, silently brooding against the unkind Baltic breeze, swilling that final glass of amontillado.

Sail away Celebrity Cruises (+44 845 456 0523; www.celebritycruises.co.uk) offers a 15-night Scandinavia and Russia cruise onboard the Celebrity Eclipse from £2,299 per person based on two sharing a balcony stateroom, including meals and entertainment. The trip departs from Southampton on 30 May 2015, calling at Copenhagen (overnight stay), Stockholm, Tallinn, St Petersburg (overnight stay), Klaipeda, Gdansk and Berlin before returning to Southampton. A suite for this sailing costs from £3,799 per person. The new Suite Class includes a private restaurant, in-room butler service and access to a VIP lounge